scholarly journals The Reconstruction of Former Ice Sheets and their Mass Balance Characteristics using a Non-Linearly Viscous Flow Model

1984 ◽  
Vol 30 (105) ◽  
pp. 140-152 ◽  
Author(s):  
G. S. Boulton ◽  
G. D. Smith ◽  
L. W. Morland
Keyword(s):  
Boundary Condition ◽  
Mass Balance ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Equilibrium Line Altitude ◽  
Isostatic Compensation ◽  
Geological Evidence ◽  
Wide Range ◽  
Terminal Zone ◽  
Subglacial Topography

AbstractA model of a non-linearly viscous ice sheet is used to investigate the influence of net mass-balance pattern, basal boundary condition, and subglacial topography on the size and shape of ice sheets. The aim is to enable geological evidence of the extent of former ice sheets to be used as indicators of palaeoclimate. A series of curves are presented showing the relationships between ice-sheet span, net mass balance, and equilibrium-line altitude (ELA) for zero and complete isostatic compensation. These are applicable to a very wide range of basal boundary conditions. The way in which they can be used to reconstruct net mass-balance gradients for former ice sheets is demonstrated. Changes in the basal boundary condition only have a strong influence on glacier span when they occur in the terminal zone. Ice-sheet expansion and contraction is not merely accompanied by changes in snow-line elevation, but also by changes in the net mass-balance gradient. The combinations of these required to cause ice-sheet expansion and contraction are analysed. A non-linearly viscous model for ice suggests that ice-sheet volume changes may not be a simple function of their change in areal extent.

scholarly journals The Reconstruction of Former Ice Sheets and their Mass Balance Characteristics using a Non-Linearly Viscous Flow Model

1984 ◽  
Vol 30 (105) ◽  
pp. 140-152 ◽  
Author(s):  
G. S. Boulton ◽  
G. D. Smith ◽  
L. W. Morland
Keyword(s):  
Boundary Condition ◽  
Mass Balance ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Equilibrium Line Altitude ◽  
Isostatic Compensation ◽  
Geological Evidence ◽  
Wide Range ◽  
Terminal Zone ◽  
Subglacial Topography

AbstractA model of a non-linearly viscous ice sheet is used to investigate the influence of net mass-balance pattern, basal boundary condition, and subglacial topography on the size and shape of ice sheets. The aim is to enable geological evidence of the extent of former ice sheets to be used as indicators of palaeoclimate. A series of curves are presented showing the relationships between ice-sheet span, net mass balance, and equilibrium-line altitude (ELA) for zero and complete isostatic compensation. These are applicable to a very wide range of basal boundary conditions. The way in which they can be used to reconstruct net mass-balance gradients for former ice sheets is demonstrated. Changes in the basal boundary condition only have a strong influence on glacier span when they occur in the terminal zone. Ice-sheet expansion and contraction is not merely accompanied by changes in snow-line elevation, but also by changes in the net mass-balance gradient. The combinations of these required to cause ice-sheet expansion and contraction are analysed. A non-linearly viscous model for ice suggests that ice-sheet volume changes may not be a simple function of their change in areal extent.

scholarly journals Thermomechanical modelling of Northern Hemisphere ice sheets with a two-level mass-balance parameterization

1995 ◽  
Vol 21 ◽  
pp. 111-116 ◽  
Author(s):  
Philippe Huybrechts ◽  
Stephen T’ Siobbel
Keyword(s):  
Surface Temperature ◽  
Mass Balance ◽  
Northern Hemisphere ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Snow Accumulation ◽  
Summer Temperature ◽  
Balance Model ◽  
Geological Evidence

A three-dimensional time-dependent thermomechanical ice-sheet model was used together with a two-level (snow-accumulation/runoff) mass-balance model to investigate the Quaternary ice sheets of the Northern Hemisphere. The model freely generates the ice-sheet geometry in response to specified changes in surface temperature and mass balance, and includes bedrock adjustment, basal sliding and a full temperature calculation within the ice. The mass-balance parameterization makes a distinction between snowfall and melting. Yearly snowfall rates depend on the present precipitation distribution, and are varied proportionally to changes in surface temperature and the moisture content of the air. The ablation model is based on the positive-degree-day method, and distinguishes between ice and snow melting. This paper discusses steady-slate characteristics, conditions for growth and retreat, and response time-scales of ice sheets as a function of a prescribed lowering of summer temperature. Most notably, the modelled extents of the Eurasian ice sheet for a summer temperature lowering of 6–7 K and of the Laurentide ice sheet for a cooling of 9–10 K are in reasonable agreement with most reconstructions based on geological evidence, except for the presence of a large ice sheet stretching from Alaska across the Bering Strait to most of eastern Siberia. In addition, wet basal conditions turned out to be always confined to the margin, whereas central areas in these reconstructions remained always cold-based. This is of relevance for processes involving reduced basal traction.

scholarly journals Thermomechanical modelling of Northern Hemisphere ice sheets with a two-level mass-balance parameterization

1995 ◽  
Vol 21 ◽  
pp. 111-116 ◽  
Author(s):  
Philippe Huybrechts ◽  
Stephen T’ Siobbel
Keyword(s):  
Surface Temperature ◽  
Mass Balance ◽  
Northern Hemisphere ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Snow Accumulation ◽  
Summer Temperature ◽  
Balance Model ◽  
Geological Evidence

A three-dimensional time-dependent thermomechanical ice-sheet model was used together with a two-level (snow-accumulation/runoff) mass-balance model to investigate the Quaternary ice sheets of the Northern Hemisphere. The model freely generates the ice-sheet geometry in response to specified changes in surface temperature and mass balance, and includes bedrock adjustment, basal sliding and a full temperature calculation within the ice. The mass-balance parameterization makes a distinction between snowfall and melting. Yearly snowfall rates depend on the present precipitation distribution, and are varied proportionally to changes in surface temperature and the moisture content of the air. The ablation model is based on the positive-degree-day method, and distinguishes between ice and snow melting. This paper discusses steady-slate characteristics, conditions for growth and retreat, and response time-scales of ice sheets as a function of a prescribed lowering of summer temperature. Most notably, the modelled extents of the Eurasian ice sheet for a summer temperature lowering of 6–7 K and of the Laurentide ice sheet for a cooling of 9–10 K are in reasonable agreement with most reconstructions based on geological evidence, except for the presence of a large ice sheet stretching from Alaska across the Bering Strait to most of eastern Siberia. In addition, wet basal conditions turned out to be always confined to the margin, whereas central areas in these reconstructions remained always cold-based. This is of relevance for processes involving reduced basal traction.

The response of large ice sheets to climatic change

1992 ◽  
Vol 338 (1285) ◽  
pp. 235-242 ◽  
Keyword(s):  
Mass Balance ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Sea Level Change ◽  
Mixing Ratio ◽  
Ice Dynamics ◽  
Environmental Models ◽  
Level Change ◽  
The Antarctic

The prediction of short-term (100 year) changes in the mass balance of ice sheets and longer-term (1000 years) variations in their ice volumes is important for a range of climatic and environmental models. The Antarctic ice sheet contains between 24 M km 3 and 29 M km 3 of ice, equivalent to a eustatic sea level change of between 60m and 72m. The annual surface accumulation is estimated to be of the order of 2200 Gtonnes, equivalent to a sea level change of 6 mm a -1 . Analysis of the present-day accumulation regime of Antarctica indicates that about 25% ( ca. 500 Gt a -1 ) of snowfall occurs in the Antarctic Peninsula region with an area of only 6.8% of the continent. To date most models have focused upon solving predictive algorithms for the climate-sensitivity of the ice sheet, and assume: (i) surface mass balance is equivalent to accumulation (i.e. no melting, evaporation or deflation); (ii) percentage change in accumulation is proportional to change in saturation mixing ratio above the surface inversion layer; and (iii) there is a linear relation between mean annual surface air tem perature and saturation mixing ratio. For the A ntarctic Peninsula with mountainous terrain containing ice caps, outlet glaciers, valley glaciers and ice shelves, where there can be significant ablation at low levels and distinct climatic regimes, models of the climate response must be more complex. In addition, owing to the high accumulation and flow rates, even short- to medium -term predictions must take account of ice dynamics. Relationships are derived for the mass balance sensitivity and, using a model developed by Hindmarsh, the transient effects of ice dynamics are estimated. It is suggested that for a 2°C rise in mean annual surface tem perature over 40 years, ablation in the A ntarctic Peninsula region would contribute at least 1.0 mm to sea level rise, offsetting the fall of 0.5 mm contributed by increased accum ulation.

scholarly journals Analysis of the surface mass balance for deglacial climate simulations

2021 ◽  
Vol 15 (2) ◽  
pp. 1131-1156
Author(s):  
Marie-Luise Kapsch ◽  
Uwe Mikolajewicz ◽  
Florian A. Ziemen ◽  
Christian B. Rodehacke ◽  
Clemens Schannwell
Keyword(s):  
Mass Balance ◽  
Northern Hemisphere ◽  
Climate Models ◽  
Ice Sheet ◽  
Meridional Overturning Circulation ◽  
Balance Model ◽  
Surface Mass Balance ◽  
Max Planck ◽  
Equilibrium Line Altitude ◽  
Surface Mass

Abstract. A realistic simulation of the surface mass balance (SMB) is essential for simulating past and future ice-sheet changes. As most state-of-the-art Earth system models (ESMs) are not capable of realistically representing processes determining the SMB, most studies of the SMB are limited to observations and regional climate models and cover the last century and near future only. Using transient simulations with the Max Planck Institute ESM in combination with an energy balance model (EBM), we extend previous research and study changes in the SMB and equilibrium line altitude (ELA) for the Northern Hemisphere ice sheets throughout the last deglaciation. The EBM is used to calculate and downscale the SMB onto a higher spatial resolution than the native ESM grid and allows for the resolution of SMB variations due to topographic gradients not resolved by the ESM. An evaluation for historical climate conditions (1980–2010) shows that derived SMBs compare well with SMBs from regional modeling. Throughout the deglaciation, changes in insolation dominate the Greenland SMB. The increase in insolation and associated warming early in the deglaciation result in an ELA and SMB increase. The SMB increase is caused by compensating effects of melt and accumulation: the warming of the atmosphere leads to an increase in melt at low elevations along the ice-sheet margins, while it results in an increase in accumulation at higher levels as a warmer atmosphere precipitates more. After 13 ka, the increase in melt begins to dominate, and the SMB decreases. The decline in Northern Hemisphere summer insolation after 9 ka leads to an increasing SMB and decreasing ELA. Superimposed on these long-term changes are centennial-scale episodes of abrupt SMB and ELA decreases related to slowdowns of the Atlantic meridional overturning circulation (AMOC) that lead to a cooling over most of the Northern Hemisphere.

scholarly journals High-resolution ice thickness and bed topography of a land-terminating section of the Greenland Ice Sheet

2014 ◽  
Vol 7 (1) ◽  
pp. 129-148 ◽  
Author(s):  
K. Lindbäck ◽  
R. Pettersson ◽  
S. H. Doyle ◽  
C. Helanow ◽  
P. Jansson ◽  
...  
Keyword(s):  
Mass Balance ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Airborne Radar ◽  
Ice Thickness ◽  
Equilibrium Line Altitude ◽  
Bed Topography ◽  
Ice Surface ◽  
Ice Sheet Dynamics

Abstract. We present ice thickness and bed topography maps with high spatial resolution (250 to 500 m) of a and-terminating section of the Greenland Ice Sheet derived from combined ground-based and airborne radar surveys. The data have a total area of ~12000 km2 and cover the whole ablation area of the outlet glaciers of Isunnguata Sermia, Russell, Leverett, Ørkendalen and Isorlersuup up to the long-term mass balance equilibrium line altitude at ~1600 m above sea level. The bed topography shows highly variable subglacial trough systems, and the trough of the Isunnguata Sermia Glacier is over-deepened and reaches an elevation of several hundreds of meters below sea level. The ice surface is smooth and only reflects the bedrock topography in a subtle way, resulting in a highly variable ice thickness. The southern part of our study area consists of higher bed elevations compared to the northern part. The covered area is one of the most studied regions of the Greenland Ice Sheet with studies of mass balance, dynamics, and supraglacial lakes, and our combined dataset can be valuable for detailed studies of ice sheet dynamics and hydrology. The compiled datasets of ground-based and airborne radar surveys are accessible for reviewers (password protected) at doi.pangaea.de/10.1594/pangaea.830314 and will be freely available in the final revised paper.

Exploring the complex uncertainties in coupled climate-ice simulations of the Last Glacial Maximum

2021 ◽  
Author(s):  
Lauren Gregoire ◽  
Niall Gandy ◽  
Lachlan Astfalck ◽  
Robin Smith ◽  
Ruza Ivanovic ◽  
...  
Keyword(s):  
Mass Balance ◽  
Last Glacial Maximum ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Glacial Maximum ◽  
Sea Surface ◽  
Surface Mass ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

<p>Simulating the co-evolution of climate and ice-sheets during the Quaternary is key to understanding some of the major abrupt changes in climate, ice and sea level. Indeed, events such as the Meltwater pulse 1a rapid sea level rise and Heinrich, Dansgaard–Oeschger and the 8.2 kyr climatic events all involve the interplay between ice sheets, the atmosphere and the ocean. Unfortunately, it is challenging to simulate the coupled Climate-Ice sheet system because small biases, errors or uncertainties in parts of the models are strongly amplified by the powerful interactions between the atmosphere and ice (e.g. ice-albedo and height-mass balance feedbacks). This leads to inaccurate or even unrealistic simulations of ice sheet extent and surface climate. To overcome this issue we need some methods to effectively explore the uncertainty in the complex Climate-Ice sheet system and reduce model biases. Here we present our approach to produce ensemble of coupled Climate-Ice sheet simulations of the Last Glacial maximum that explore the uncertainties in climate and ice sheet processes.</p><p>We use the FAMOUS-ICE earth system model, which comprises a coarse-resolution and fast general circulation model coupled to the Glimmer-CISM ice sheet model. We prescribe sea surface temperature and sea ice concentrations in order to control and reduce biases in polar climate, which strongly affect the surface mass balance and simulated extent of the northern hemisphere ice sheets. We develop and apply a method to reconstruct and sample a range of realistic sea surface temperature and sea-ice concentration spatio-temporal field. These are created by merging information from PMIP3/4 climate simulations and proxy-data for sea surface temperatures at the Last Glacial Maximum with Bayes linear analysis. We then use these to generate ensembles of FAMOUS-ice simulations of the Last Glacial maximum following the PMIP4 protocol, with the Greenland and North American ice sheets interactively simulated. In addition to exploring a range of sea surface conditions, we also vary key parameters that control the surface mass balance and flow of ice sheets. We thus produce ensembles of simulations that will later be used to emulate ice sheet surface mass balance.  </p>

scholarly journals Erosion by Continental Ice Sheets

1979 ◽  
Vol 23 (89) ◽  
pp. 401-402
Author(s):  
I. M. Whillans
Keyword(s):  
Mass Balance ◽  
Short Distance ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Present Theory ◽  
Frictional Heat ◽  
Break Up ◽  
Basal Melting ◽  
Continental Ice Sheets

Abstract Some of the problems with earlier theories for erosion and transport by ice sheets are discussed, and it is noted that those theories cannot simply account for the often-reported finding that most till is derived from bedrock only a few tens of kilometers up-glacier. Considerations of the mass balance of debris in transport lead to the conclusion that ice sheets are capable of transporting most debris only a short distance. The theory that the break-up of bedrock is mostly a preglacial process is developed. The advancing ice sheet collects the debris and then deposits it after a short travel. As the ice sheet first advances over the regolith, debris is frozen onto the base and is carried until basal melting due to geothermal and frictional heat causes lodgment till deposition. Most debris is deposited during the advance of the ice sheet and is carried only a short distance. A generally small amount of debris is carried at higher levels and is deposited during ice standstill and retreat as melt-out and ablation tills. The present theory makes many predictions, among them, that most till units are not traceable over long distances, that thick till sequences represent unstable glacier margins and not necessarily long periods of glacier occupation, and that lodgment tills are to be interpreted in terms of ice advances and ablation tills in terms of ice retreats. This paper is published in full in Journal of Geology, Vol. 86, No. 4, 1978, p. 516–24.

scholarly journals Basal Sliding Relations Deduced from Ice-Sheet Data

1984 ◽  
Vol 30 (105) ◽  
pp. 131-139 ◽  
Author(s):  
L. W. Morland ◽  
G. D. Smith ◽  
G. S. Boulton
Keyword(s):  
Boundary Condition ◽  
Mass Balance ◽  
Large Scale ◽  
Ice Sheet ◽  
Lower Boundary ◽  
Tangential Velocity ◽  
Greenland Ice Sheet ◽  
Overburden Pressure ◽  
Ice Flow ◽  
Surface Mass

AbstractThe sliding law is defined as a basal boundary condition for the large-scale bulk ice flow, relating the tangential tractionτb, overburden pressurepb, and tangential velocityubon a smoothed-out mean bed contour. This effective bed is a lower boundary viewed on the scale of the bulk ice flow and is not the physical ice/rock or sediment interface. The sliding relation reflects on the same scale the complex motion taking place in the neighbourhood of the physical interface. The isothermal steady-state ice-sheet analysis of Morland and Johnson (1980, 1982) is applied to known surface profiles from the Greenland ice sheet and Devon Island ice cap, with their corresponding mass-balance distributions, to determineτb,pb, andubfor each case. These basal estimates are used in turn to construct, using least-squares correlation, polynomial representations for an overburden dependenceλ(pb) in the adopted form of sliding lawτb═λ(pb)ub1/mwithm ≥1.The two different data sets determine functionsλ(pb) of very different magnitudes, reflecting very different basal conditions. A universal sliding law must therefore contain more general dependence on basal conditions, but the two relations determined appear to describe the two extremes. Hence use of both relations in turn to determine profiles compatible with given mass-balance distributions can be expected to yield extremes of the possible profiles, and further to show the sensitivity of profile form to variation of the sliding relation. The theory is designed as a basis for reconstruction of former ice sheets and their dynamics which are related to the two fundamental determinants of surface mass balance and basal boundary condition.

scholarly journals Evolution of the large-scale atmospheric circulation in response to changing ice sheets over the last glacial cycle

2014 ◽  
Vol 10 (4) ◽  
pp. 1453-1471 ◽  
Author(s):  
M. Löfverström ◽  
R. Caballero ◽  
J. Nilsson ◽  
J. Kleman
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Glacial Cycle ◽  
Mean Flow ◽  
Geological Evidence ◽  
Last Glacial ◽  
The Last Glacial

Abstract. We present modelling results of the atmospheric circulation at the cold periods of marine isotope stage 5b (MIS 5b), MIS 4 and the Last Glacial Maximum (LGM), as well as the interglacial. The palaeosimulations are forced by ice-sheet reconstructions consistent with geological evidence and by appropriate insolation and greenhouse gas concentrations. The results suggest that the large-scale atmospheric winter circulation remained largely similar to the interglacial for a significant part of the glacial cycle. The proposed explanation is that the ice sheets were located in areas where their interaction with the mean flow is limited. However, the LGM Laurentide Ice Sheet induces a much larger planetary wave that leads to a zonalisation of the Atlantic jet. In summer, the ice-sheet topography dynamically induces warm temperatures in Alaska and central Asia that inhibits the expansion of the ice sheets into these regions. The warm temperatures may also serve as an explanation for westward propagation of the Eurasian Ice Sheet from MIS 4 to the LGM.

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